This disclosure relates to an exhaust system and to thermal energy management and more particularly relates to management of thermal energy flowing into and out of engine exhaust components.
The elimination of hydrocarbons, carbon monoxide, soluble organic fraction, nitric oxide, nitrogen dioxide, nitrous oxide, sulfur oxides, sulfurous oxides, hydrogen sulfide, ammonia and particulates in exhaust gas is a widely addressed problem as a result of environmental concerns and mandated government emissions regulations.
Diesel particulate filters collect particulates from exhaust gas streams. A problem with diesel particulate filters is that they gradually become clogged with particulate matter impeding exhaust flow. The impeded exhaust flow increases pressure back through the exhaust valves into the engine cylinders. This excessive backpressure results in poor engine performance and poor fuel economy. Particulate matter typically consists of carbon, heavy organics, sulfur compounds, nitrogen compounds and phosphorous compounds.
Regeneration of diesel particulate filters occurs when diesel engines emit an exhaust gas stream at a high enough temperature to burn out particulate matter. High temperature exhaust is generated at high engine speeds. However, many passenger diesel vehicles are operated for protracted periods of time at, or close to, idling speed. At idle speed the exhaust gas stream is below the combustion temperature of particulate matter.
Passive diesel particulate filters are used in heavy duty applications that generate enough exhaust temperature for effective regeneration. However passive diesel systems regenerate particulate traps, but do little for NOx reduction. Further, while passive diesel particulate traps effectively remove coarse particulates, the nano-phase particulates are greatly increased when a passive regeneration is used. An effective active regeneration method is greatly desired. Especially for acceptance of lean bum passenger vehicles.
The doping of diesel fuels with diesel combustion aids is an effective active regeneration method for small passenger vehicles. The combustion additive lowers engine out particulates then collects as an oxide on the particulate trap. Further, the collected oxide aids in the combustion of trapped particulates at lower temperatures. However, particulate oxides cannot pass through the particulate trap. And the particulate oxides are rapidly poisoned by engine oil deposits and become “vitrified”. Eventually, at relatively low hours of engine use, the particulate trap has to be physically removed and vitrified particulate oxides removed. Stricter emission standards make particulate trap cleaning during the useful life of a vehicle undesirable if not unacceptable.
The most common particulate trap and catalyst deactivation occurs because vaporized engine oils decompose and form diffusion limiting glass coatings. For example, most engine oil contains zinc dialkyl phosphate and calcium phosphate. The materials form the glass zinc calcium phosphate over particulate traps, catalysts and sensors. Eventually particulate traps cannot be regenerated because the glass layer cannot be vaporized.
What is needed in the art is a system and method for the regeneration of particulate traps that does not adversely affect a NOx adsorber disposed downstream of the particulate trap.